Temperature calibration of the E and B experiment

TL;DR

The paper details the temperature calibration process of the EBEX balloon-borne polarimeter, including gain response calibration and optical parameter determination, to ensure accurate measurements of cosmic microwave background polarization.

Contribution

It introduces a two-step iterative calibration method combining Galactic plane signals and star camera data for precise temperature calibration of a balloon-borne experiment.

Findings

Calibration process converges after iterative refinement.

Effective smoothing scale and offset angles are accurately determined.

Calibration improves measurement accuracy of polarization data.

Abstract

The E and B Experiment (EBEX) is a balloon-borne polarimeter designed to measure the polarization of the cosmic microwave background radiation and to characterize the polarization of galactic dust. EBEX was launched December 29, 2012 and circumnavigated Antarctica observing $\sim$6,000 square degrees of sky during 11 days at three frequency bands centered around 150, 250 and 410 GHz. EBEX was the first experiment to operate a kilo-pixel array of transition-edge sensor bolometers and a continuously rotating achromatic half-wave plate aboard a balloon platform. It also pioneered the use of detector readout based on digital frequency domain multiplexing. We describe the temperature calibration of the experiment. The gain response of the experiment is calibrated using a two-step iterative process. We use signals measured on passes across the Galactic plane to convert from readout-system counts to power. The effective smoothing scale of the EBEX optics and the star camera-to-detector offset angles are determined through \c{hi}2 minimization using the compact HII region RCW 38. This two-step process is initially performed with parameters measured before the EBEX 2013 flight and then repeated until the calibration factor and parameters converge.